1. Field of the Invention
The present invention relates generally to the field of ceramic materials and more specifically to pigmented silicon nitride useful in the manufacture of semiconductor materials.
2. Prior Art
There are advanced ceramic materials that are now required by suppliers of semiconductor processing equipment--the equipment used to manufacture integrated circuits. The need for these new ceramics is primarily driven by chip makers seeking process solutions for 0.25, 0.18 and even finer micron line geometry designs. In part, these solutions require aggressive environments which preclude the use of many traditional materials as structural components in processing chambers. These chambers perform individual unit process steps such as chemical vapor deposition (CVD), plasma etching, rapid thermal processing (RTP), etc.
There are certain types of non-oxide ceramics that have been specifically engineered for these new semiconductor processing applications. One such ceramic is a carefully defined grade of silicon nitride that appears to be very useful as a structural component(s) in plasma etching chambers--a highly corrosive/erosive fluorine gas environment. This application requires a hot pressed grade of silicon nitride that is extremely pure and is very near theoretical density. Unfortunately, this type of silicon nitride, in its natural state, is very light in color and therefore very difficult to manufacture so that the final appearance of the material is cosmetically pure, that is, uniform in a single color particularly if the part is large. Color uniformity is a strict requirement by the semiconductor industry in that it implies quality and manufacturing consistency.
Color uniformity in that fine grade of silicon is very difficult to achieve for many reasons. Reasons for manufactured non-uniformity include:
1) Small chemical variations within the material's grain boundary; PA1 2) The secondary phase, or grain boundary phase, is not uniformly amorphous or not uniformly crystalline; PA1 3) Random formation of silicon crystallites during manufacturing; PA1 4) Preferential solution of carbon or a carbon compound(s) during material processing; and PA1 5) Clustering of micro-porosity within the microstructure of the material thereby producing random color centers.
What is needed is a relatively inexpensive way to chemically pigment the silicon nitride so that its appearance upon manufacturing is uniformly dark, preferably black (most discoloration in silicon nitride is gray to black). Furthermore, the pigment must be chemically and physically inert within the application process. That is, the pigment cannot chemically "react" with the product being produced nor can it cause the generation of particulate during process operation. The pigment can, however, react with the fluorine based gas/plasma in such a manner that the reaction product remains a gas and is therefore "swept out" of the chamber with the fluorine during chamber purging. Again, this gaseous reaction product cannot negatively affect the performance of the process or the manufactured product. It must be totally benign with respect to the process.